Examine the effect of natural menopause and of therapy with estrogen and progesterone on energy expenditure in healthy women. 24-h energy expenditure is measured twice using the metabolic chamber, and resting metabolic rate and diet-induced thermogenesis are assessed twice using the metabolic cart. EE measurements by both methods are carried out on postmenopausal subjects at baseline and after 3 months of placebo. EE is assessed in 10 premenopausal women.